The objective of this research is to identify the biochemical mechanisms involved in the acute toxicity of organotin compounds in mammals. The authors propose that some of the organotin compounds are toxic to mammals because of effects on the activity of membrane associated adenosine triphosphatase activities; these effects are postulated to result in changes in the kinetics of such biologically important processes as the active transport of solutes across biomembranes and mitochondrial oxidative phosphorylation. This hypothesis will be tested by: (1) further investigation of the effects of the organotin compounds on the function of isolated mitochondria; (2) comparing the effects of some organotin compounds on the adenosine triphosphatase activity of kidney cell membranes with the effects of these compounds on kidney function in vivo; (3) comparing the hemolytic activity of organotin compounds with the ability of these compounds to inhibit the adenosine triphosphatase activity of red cell preparations.